1. Field of the Invention
The present invention relates to a dishwasher comprising a circulating pump, a washing tank provided with a substantially horizontal filter disposed in the path of water flow drawn by the circulating pump and rotating spray means capable of directing downwardly at least one water jet.
2. Description of the Related Art
It is well known that the water jet directed downward be used mainly for cleaning automatically the above filter and any other coarse filter eventually associated to such horizontal filter. Another possible function of such water jet is to drive the rotation of the spray arm, even if for such function other water jets may be used. With the very efficient spray systems of modern dishwashers the speed of water jets is very high. If this is good for the water jets directed towards the crockery to be washed, it makes problem in its impingement against the fine-mesh horizontal filter placed below the spray arm, since such impingement creates many air bubbles which are driven in the chamber below the filter and sucked by the circulating pump. The presence of air bubbles in the water flow drawn by the circulating pump makes the working of this latter very unstable, since the rotational speed of the impeller can have quick increase and subsequent quick decrease. In order to avoid such unstable working (with consequent damages to the electric motor), it is known to have a high water level in the chamber so that the air bubbles have sufficient time to reach the surface without being sucked by the pump. This of course requires a higher amount of water per fill, which is not desirable in view of detergent concentration, impact on environment and energy needed for water heating.
A known solution is to provide a screen disposed between the spray arm and the substantially horizontal filter for intercepting the water jet above such filter. This solution has the drawback of requiring an additional component of the dishwashing machine, with higher overall cost and an uneasy removal of the spray arm and the filter for cleaning thereof. Moreover the interception of the downwardly directed water flow totally prevents the cleaning action on the fine-mesh filter.
In accordance with the invention there is provided a dishwasher in which the substantially horizontal filter presents a not uniform percentage of open area. Preferably an area of the filter below a circular pattern of the downwardly directed jet presents a percentage of open area lower than the percentage of open area of the remaining portions of the filter.
Thanks to such technical feature, air suction toward the circulating pump is avoided so that a smooth pump operation is assured (high pump stability). Since air is no longer brought to the pump suction area, the water level can be lowered, which means lower water amount per fill.